The present invention relates to a gas spring apparatus, and more specifically, to an improvement of a gas spring apparatus having an oil chamber and a gas chamber therein.
Prior art gas spring apparatuses, which are adapted to contain oil and gas, comprise a cylinder housing and a rod fitted therein. A gas chamber and an oil chamber are defined inside the cylinder housing. Compressed gas, such as nitrogen gas, is sealed in the gas chamber. The repulsive force of the gas functions as a gas spring. Damping force generating means is provided inside the cylinder housing. The oil in the oil chamber is subjected to viscous resistance as it passes through the generating means, so that reciprocation of the rod is damped.
In the conventional gas spring apparatuses, a free piston is disposed between the oil and gas chambers, in order to prevent the gas in the gas chamber from leaking into the oil in the oil chamber. In these apparatuses using the free piston, however, a great frictional resistance is produced at a seal portion, as the piston moves. Moreover, the gas is liable to leak out from the gas chamber, through the seal portion of the piston. Thus, it is difficult to completely prevent the gas from leaking into the oil.
As disclosed in U.S. Pat. No. 3,469,661 or 3,587,789, a gas spring apparatus has been proposed which uses a flexible cylindrical bladder. However, the conventional bladder cannot satisfactorily prevent the gas in the gas chamber from penetrating into the oil chamber. Therefore, prolonged use of the apparatus may possibly cause a gas leak, which results in a reduction in capacity of the gas chamber. If the gas chamber capacity is reduced in this manner, the spring constant of the apparatus increases. Thus, if the gas spring apparatus is used for a suspension system of an automobile, the vehicle becomes less comfortable to ride in, and its height is lowered. To avoid this, gas must be resupplied to the gas chamber inside the cylinder housing. The gas resupply, however, requires considerable labor.